THE INFLUENCE OF SR(CA)₂NB₂O₇ ON THE PHASE FORMATION AND THE STRUCTURE OF SOLID SOLUTIONS BASED ON THE SODIUM-KALIUM NIOBATE

(1- x )KNbO₃ - x NaNbO₃ system is one of the most learned among lead-free ceramics. This system is promising for potential use in piezoelectric technology and the replacement of lead-containing elements in such devices. However, despite many works aimed at the solution of this problem, at the moment, no lead-free materials with the properties comparable to the lead-containing piezo-ceramics were produced. It is caused by various technological difficulties of creating solid solutions (SS) based on the lead-free compositions such as alkaline components volatility and the strongest dependence of the observed properties on the production conditions (thermodynamic history). One of the techniques applied to improve processability and SS stability as well as to improve electrophysical properties is modifying. The paper deals with the study of the influence of calcium and strontium pyroniobates additives on the structure and properties of (1- x )KNbO₃ - x NaNbO₃ system. The conditions of synthesis and sintering for each solid solution of (1- x-у )KNbO₃ - y NaNbO₃ - x (Sr/Са)₂Nb₂O₇ systems are optimized. The author carried out the X-ray diffraction and radiographic analysis of the produced items, analyzed the dependence of the parameters, cell volume, and the ceramics densities on the concentration of added (Sr/Са)₂Nb₂O₇ component. The study determined that the increase in the content of calcium and strontium pyroniobates in the interval of 0≤х≤10 % leads to the appearance of several phase transitions caused by the structural transformation in the (1- x-у )KNbO₃ - y NaNbO₃ - x (Sr/Са)₂Nb₂O₇ systems. The symmetry of the abovementioned systems changes in different ways. The doping with strontium pyroniobate causes the tetragonal structure distortion and the doping with calcium pyroniobate leads to the formation of the cubic lattice. The study showed as well that the adding of (Sr/Са)₂Nb₂O₇ pyroniobates to the (1- x )KNbO₃ - x NaNbO₃ system above 2.5 % significantly reduces the density of the produced ceramics.

(1-x)KNbO₃ - xNaNbO₃, functional materials, solid solutions, environmentally-friendly materials, solid-phase synthesis, phase formation, ceramics sintering, cell symmetry, phase transition, ceramics density, piezoelectric properties, (1-x)KNbO₃ - xNaNbO₃